The primary objective of this study is to compare the safety and efficacy of MEDI-493 (15mg/kg) to placebo when administered monthly by intramuscular injection for the reduction of the incidence of RSV hospitalization among infants born prematurely and infants with bronchopulmonary dysplasia (BPD). The secondary objectives of the study are to determine the effect of monthly MEDI-493 prophylaxis compared to placebo on RSV hospitalization parameters: total RSV hospital days, total RSV hospital days with increased supplemental oxygen requirement, total RSV hospital days with moderate or severe lower respiratory tract infection (LRI score >/= 3), frequency and total RSV-associated ICU days, frequency and total days of RSV-associated mechanical ventilation, incidence and total days of hospitalization for non-RSV respiratory disease and any respiratory disease and hospitalization for any cause, incidence of otitis media.